The nation's airlines continue to pack passengers on domestic flights at record rates by limiting the number of seats and planes they add as demand grows, according to the latest federal data.

The percentage of filled seats on domestic flights grew to 85.5% in March, a record high for that month, up from the previous peak of 85% in March 2013, according to data released Thursday by the U.S. Bureau of Transportation Statistics.

Rating: 70 out of 100.In the American Customer Satisfaction Index, passengers gave all the airlines not specifically named in this gallery, such as Virgin America and Alaska Airlines, a combined rating of 70.

Rating: 70 out of 100.In the American Customer Satisfaction Index, passengers gave all the airlines not specifically named in this gallery, such as Virgin America and Alaska Airlines, a combined rating of 70. (Michael Robinson Chavez / Los Angeles Times)

The demand for domestic flights grew 2.5% in March, compared with the same month in 2013, while the number of added seats grew by 2%, according to the bureau.

Meanwhile, federal data show that the U.S.-based airline industry has added 5% more seating capacity on international flights in March, while demand grew by 0.9%, compared with March 2013.

As a result, travelers are more likely to find empty seats on high-priced international flights. The percentage of seats filled on international flights dropped to 79.2% in March from 82.5% in March 2013.

Since the end of the recession, the airline industry has been very cautious about adding extra seats and more planes in the face of growing demand, according to industry experts.

"There's a lot of pent-up demand still, and airlines have kept capacity in check," said George Hobica, founder of Airfarewatchdog.com, a low-airfare alert and air travel advice website. "It certainly means that if you miss your flight or it's canceled you may have more trouble finding a seat on the next flight out."

The strategy has paid off, with U.S.-based airlines reporting a combined net income of $12.7 billion in 2013, compared with $98 million in 2012, according to the Bureau of Transportation Statistics.

To read more about travel, tourism and the airline industry, follow me on Twitter at @hugomartin.